[villagetinker]

While we are full time, a couple of questions. Do you use a home management firm to check on your house while you are away? Do have the humidistat set while you are here? There are a lot of molds and pollen, and in another thread there were complaints about sinus problems late last year. You did not state the type of sickness, could this be an allergy? If the house is sitting empty for several years, and now 6 months at a time, you may have a significant dust problem. Have you changes the air filter in the A/C at least once per year, possibly twice per year, depending to the system. Did you check the drain on the A/C, if it is blocked, you can easily get mold in the air handler where the filter is located. Have you tried opening the house and completely airing it out when you come down?
No real good answers, but hope this helps.